1. Field of the Invention
The invention relates to the field of guided missiles and more specifically relates to a control device using gas jets making it possible to modify the flight path or trajectory of a missile.
2. Description of the Prior Art
A guided missile more paticularly comprises propulsion means operating over all or part of the flight path of the missile, guidance means for measuring errors in the trajectory of the missile compared with the position of a designated target and control means enabling the correction of these errors in order to minimize the distance by which the missile passes to the side of the target.
The correction in the errors of the trajectory of a guided missile, rocket or the like can be brought about by applying, at a predetermined point of said missile, a lateral thrust force, i.e. a thrust force perpendicular to the longitudinal axis of the missile body. This thrust force can be supplied by the discharge of a flow of material whose orientation and optionally intensity can be modified. This flow of material is generally a gas flow.
A control device using gas jets, more specifically intended for modifying the flight direction of a missile comprises a primary energy source which generates a gas flow, a set of fixed nozzles appropriately distributed over the missile body and means making it possible to divert this gas flow towards one of these nozzles in accordance with control instructions available on board the missile and resulting from measured trajectory errors. In certain applications of guided missiles it is necessary during the flight phase to jointly have an axial thrust force with a view to maintaining the speed of travel of the missile, and a transverse thrust force in order to modify the flight direction of the missile. This can be obtained by inclining the discharge nozzles towards the rear of the missile and consequently increasing the gas flow rate.
Control devices using gas jets can utilize a primary energy source, such as a liquid propellant, which supplies a combustion chamber for providing a gas flow. The use of a liquid propellant ensures great operating flexibility, but makes the construction more complex and reduces the possible storage time. Thus, in most uses for guided missiles, preference is given to control devices employing a solid propellant.
A difficulty which is inherent in solid propellants is that once combustion has been started, the latter must be maintained at a relatively constant gas flow rate. Thus, an increase in the flow rate would lead to flame-out and conversely a reduction in the flow rate would lead to a prohibitive increase in the combustion pressure and therefore to the explosion of the combustion chamber. It is therefore vital for a control device using a solid propellant to operate with a continuous gas flow rate, which only varies within limits compatible with the propellant used.
A problem which arises in connection with the design of a control device using gas jets is to ensure that the direction of the thrust forces passes through the same point advantageously located in the vicinity of the center of gravity of the missile and that the displacement of this center of gravity during the operation of the device only varies to a very limited extent. This center of gravity displacement phenomenon, resulting from the combustion of the propellant becomes more sensible as the propellant mass or weight increases.
French Pat. No. 77 10755, filed on Apr. 8, 1977 by the Applicant Company, discloses a control device using gas jets operating with a continuous, constant gas flow rate. According to an embodiment described therein, the control device comprises two gas generators operating in parallel and a set of four lateral fixed nozzles arranged in ring form on the missile body. These nozzles are connected by gas conduits to a common inlet in which is positioned a vane with four branches articulated on a ball joint. The controlled movements of this vane makes it possible to divert the gas flow into two adjacent nozzles, which are simultaneously open.